How important is external amp gain?

[VMPS-TIII]

@PENG or others? I am using the Denon 4700 in pre-amp mode and external amplification. How important is the gain level of the external amp and what would be ideal for the Denon 4700 in pre-amp mode? Thank you!

 

[M Code]

Matching amplifier gain to preamplifier output level is crucial but often overlooked....
For many years, the industry norm for pre-out level was 1V RMS for consumer products and 1.4V RMS for pro-auto products. Next because pro-audio amplifiers became popular due to a strong watts per $ ratio connected to consumer products. So the complaint was often posted the AVR didn't have enough pre-out level to drive the power amplifier to its rated output. Fast-Forward to now, largely corrected as of now many of the pro-audio power amplifiers have switchable input sensitivity... I recall the Denon has adequate pre-out level but the key question is.. What power amplifier are U intending to connect to? Double check its input sensitivity spec..

Just my $0.02...

 

[VMPS-TIII]

Matching amplifier gain to preamplifier output level is crucial but often overlooked....
For many years, the industry norm for pre-out level was 1V RMS for consumer products and 1.4V RMS for pro-auto products. Next because pro-audio amplifiers became popular due to a strong watts per $ ratio connected to consumer products. So the complaint was often posted the AVR didn't have enough pre-out level to drive the power amplifier to its rated output. Fast-Forward to now, largely corrected as of now many of the pro-audio power amplifiers have switchable input sensitivity... I recall the Denon has adequate pre-out level but the key question is.. What power amplifier are U intending to connect to? Double check its input sensitivity spec..

Just my $0.02...

I have a Monolith 7x200 now with a voltage gain of 28dB and specs say Input Sensitivity for Full Rated Power is 1.6 volts. It seems to work fine.

I was thinking of purchasing a 1ET400A Purifi based Amplifier that has 26dB gain that the manufacturer says can be set at the factory to whatever setting I prefer.

I'm not sure if the 26dB on the 1ET400A vs the 28dB on the Monolith7x200 makes a difference? Should I ask for the gain on the 1ET400A be increased to 30 or 28dB or just order it at the factory 26dB setting?

I'm also having difficulty finding the spec for the Denon 4700 preamp output.

 

[WaynePflughaupt]

I’d suggest simply matching the gain of the new amp to the gain of the Denon’s internal amp. Easy instructions here:

Gain Structure for Home Theater: Getting the Most from...

www.hometheatershack.com

Regards,
Wayne A. Pflughaupt

 

[VMPS-TIII]

So I read this 3700 review. It says, "So when selecting an external amplifier for channels beyond fronts, make sure it can output its maximum power at or below 1.4 volts (usually specified as "sensitivity")."

Denon AVR-X3700H AVR Review

This is a review and detailed measurements of Denon AVR-X3700H 9.2 channel 8K Home Theater AV Receiver (AVR). It is kindly loaned to me by a local member and costs US $1,199. Visually, if you have seen one AVR, you have seen the look of the AVR-X3700H: The input selector is plastic and...

www.audiosciencereview.com

Based on that information, it's possible the Denon preamp may not be able to fully power the Monolith 7X200 to it's maximum? I say that as Input Sensitivity spec for Full Rated Power is 1.6 volts on the Monolith 7X200. That's not to say it won't work, just that it may not effectively reach maximum power?

If the amp had a gain of 30-32dB would that over come the issue and create a slightly better match? Or could the increased gain cause additional distortion?

 

[Irvrobinson]

I have a Monolith 7x200 now with a voltage gain of 28dB and specs say Input Sensitivity for Full Rated Power is 1.6 volts. It seems to work fine.

I was thinking of purchasing a 1ET400A Purifi based Amplifier that has 26dB gain that the manufacturer says can be set at the factory to whatever setting I prefer.

I'm not sure if the 26dB on the 1ET400A vs the 28dB on the Monolith7x200 makes a difference? Should I ask for the gain on the 1ET400A be increased to 30 or 28dB or just order it at the factory 26dB setting?

I'm also having difficulty finding the spec for the Denon 4700 preamp output.

If I'm reading the 4700 owners manual correctly, it says on page 333 that the output voltage is rated at 1.2v. That's pretty low, but unless you have very inefficient speakers I can't believe it won't work well. How efficient are your speakers?

 

[VMPS-TIII]

If I'm reading the 4700 owners manual correctly, it says on page 333 that the output voltage is rated at 1.2v. That's pretty low, but unless you have very inefficient speakers I can't believe it won't work well. How efficient are your speakers?

I see what you are referring to. The speakers will vary from 85-90dB sensitivity. What I was trying to understand is with the Denon preamp output being in the 1.2 to 1.4V range what would be the ideal gain level spec to look for in an external amp.

It doesn't make much sense to purchase a 400W amp that can only provide 250W as a result of the Denon output voltage and the amp gain level mis-match?

 

[PENG]

I have a Monolith 7x200 now with a voltage gain of 28dB and specs say Input Sensitivity for Full Rated Power is 1.6 volts. It seems to work fine.

I was thinking of purchasing a 1ET400A Purifi based Amplifier that has 26dB gain that the manufacturer says can be set at the factory to whatever setting I prefer.

I'm not sure if the 26dB on the 1ET400A vs the 28dB on the Monolith7x200 makes a difference? Should I ask for the gain on the 1ET400A be increased to 30 or 28dB or just order it at the factory 26dB setting?

I'm also having difficulty finding the spec for the Denon 4700 preamp output.

I thought your questions have been answered many times over a ASR and AH. Anyways, if you have the AVR-X4700H paired with the Monolith 200 W amp you should be fine. Below are some facts:

Monolith 200 W amp gain is 28 dB
Denon/Marantz AVR gain is about 29 dB

Amir comments on needing more than 1.4 V for amps like the Monolith was based on not using preamp mode. If you use preamp mode, the power amp section's inputs are disconnected from the AVR preamp/proc outputs so the pre out signal will remain very clean to > 2V.

The Denon/Marantz specs say 1.2 V rated, but we don't know their basis, it could just mean 1.2 V when the internal amps are driven to their maximum output, but we can only guess. In the service manual it shows pre out maximum 4.2 V maximum. In the THD+N vs output graph they sent Gene, it also show >4 V, so you have nothing to worry about.

In the ASR review, the SINAD vs Measured level graph tells you all you need to know:

Denon AVR-X4700 AVR Review (Updated)

This is a second review of the Denon AVR-X4700 AVR. It was kindly purchased by a member and drop shipped to me. It costs US $1,700 from Amazon including free shipping. I will explain the reason for the revision in a bit. For now, I will cut and paste some of the information from the first...

www.audiosciencereview.com

 

[VMPS-TIII]

I thought your questions have been answered many times over a ASR and AH. Anyways, if you have the AVR-X4700H paired with the Monolith 200 W amp you should be fine. Below are some facts:

Monolith 200 W amp gain is 28 dB
Denon/Marantz AVR gain is about 29 dB

Amir comments on needing more than 1.4 V for amps like the Monolith was based on not using preamp mode. If you use preamp mode, the power amp section's inputs are disconnected from the AVR preamp/proc outputs so the pre out signal will remain very clean to > 2V.

The Denon/Marantz specs say 1.2 V rated, but we don't know their basis, it could just mean 1.2 V when the internal amps are driven to their maximum output, but we can only guess. In the service manual it shows pre out maximum 4.2 V maximum. In the THD+N vs output graph they sent Gene, it also show >4 V, so you have nothing to worry about.

@PENG - so you think whether the external amp gain is 28 or 26 it makes not difference with the Denon 4700?

 

[Irvrobinson]

I see what you are referring to. The speakers will vary from 85-90dB sensitivity. What I was trying to understand is with the Denon preamp output being in the 1.2 to 1.4V range what would be the ideal gain level spec to look for in an external amp.

It doesn't make much sense to purchase a 400W amp that can only provide 250W as a result of the Denon output voltage and the amp gain level mis-match?

Unless you have a very large room, large speakers with at least three drivers (and probably more), and you're listening at very high volumes (e.g. 85db average volume at your listening seat), I doubt very much that even deep bass in action movies will draw within 3db of 400w/ch. And that's assuming you're not using subwoofers and a typical 80Hz crossover. Are you using subs?

That said, I have personally experienced a gain mismatch in my HT system. I had an Outlaw 975 prepro which drove an ATI AT602 amp. The amp has a voltage gain of 24db. When I got the prepro I was using the amp to drive a pair of JBL monitors that were rather low sensitivity, about 84db/2.83v/1m, and the prepro couldn't drive the amp to provide adequate power to the speakers. It was very annoying. Outlaw and I had a conversation about it. Some time later I swapped out the JBLs for a pair of Klipsch RF62ii speakers that were probably 8-10db more sensitive, and much more efficient. Problem solved.

The point is that you have to consider the entire signal path to judge if the component combination will be acceptable, and the only way to really know is to try it.

 

[PENG]

@PENG - so you think whether the external amp gain is 28 or 26 it makes not difference with the Denon 4700?

I would never say that!

Use 1.4 V as example:

1.4 V input to a power amp with 28 dB gain, power amp output will be about 154.6 W

1.4 V input to a power amp with 26 dB gain, power amp output will be about 97.5 W.

The difference is not insignificant.

For a 200 W rated (8 Ohms) power amp, you need 2 V input to use its full rated output. So whether that matters or not, depends on the power you need. That's why it is important to take the first step, that is to figure out your power need, before shopping for power amps for you AVRs, or even AVPs.

 

[VMPS-TIII]

I would never say that!

Use 1.4 V as example:
1.4 V input to a power amp with 28 dB gain, power amp output will be about 154.6 W

1.4 V input to a power amp with 26 dB gain, power amp output will be about 97.5 W.

The difference is not insignificant.

For a 200 W rated (8 Ohms) power amp, you need 2 V input to use its full rated output. So whether that matters or not, depends on the power you need. That's why it is important to take the first step, that is to figure out your power need, before shopping for power amps for you AVRs, or even AVPs.

@PENG - I'm not really concerned about the 200W Monolith7 with 28dB gain. I'm using it and it works fine.

But the Purifi 1ET400A based amp I am looking at offers 400W per channel into 4 ohms but only has a 26dB gain. It's a 2 channel amp. The builder says he can increase the gain higher if it would be better for my configuration.

I have two questions:

1. What would be the math to determine what the ext amp gain should be to produce 400W with a 1.4V signal from the Denon 4700?

2. Could increasing the ext amp gain increase distortion on the Purifi 1ET400A based amp?

Thank you!

 

[Kleinst]

I thought your questions have been answered many times over a ASR and AH. Anyways, if you have the AVR-X4700H paired with the Monolith 200 W amp you should be fine. Below are some facts:

Monolith 200 W amp gain is 28 dB
Denon/Marantz AVR gain is about 29 dB

Amir comments on needing more than 1.4 V for amps like the Monolith was based on not using preamp mode. If you use preamp mode, the power amp section's inputs are disconnected from the AVR preamp/proc outputs so the pre out signal will remain very clean to > 2V.

The Denon/Marantz specs say 1.2 V rated, but we don't know their basis, it could just mean 1.2 V when the internal amps are driven to their maximum output, but we can only guess. In the service manual it shows pre out maximum 4.2 V maximum. In the THD+N vs output graph they sent Gene, it also show >4 V, so you have nothing to worry about.

In the ASR review, the SINAD vs Measured level graph tells you all you need to know:

Denon AVR-X4700 AVR Review (Updated)

This is a second review of the Denon AVR-X4700 AVR. It was kindly purchased by a member and drop shipped to me. It costs US $1,700 from Amazon including free shipping. I will explain the reason for the revision in a bit. For now, I will cut and paste some of the information from the first...

www.audiosciencereview.com

View attachment 41675

Good question and one I have thought of. Is this another reason why we might at times not see a dramatic impact from having a separate AMP from an AVR relative to using the internal AVR AMPS? If the AMP requires a higher input level than the AVR traditionally puts out, do we lose some of the upside from a 200WPC amp say vs the AVR around 130-140 etc.? Is there any loss that can occur between the AVR and the AMP that wouldn't be lost just pushing from the AVR AMPS

And as you state, people like me would only have a spec number to go off so it's hard to tell.

I still like my external AMP so I won't change regardless but often wondered

This might not make sense but if so, would love to see if you have any thoughts

 

[slipperybidness]

You have gotten good answers here. A key detail is that you need to be looking at the entire gain structure from input to output, not just the gain of the amp.

I do want to add some specific details about amp gain and answer your questions about the 26dB figure.

26dB amp stage gain is indeed a bit on the low end. If you are getting this built and can select your gain, something in the range of 29-32dB would be much more typical. When I set gain with a DIY design, this is the exact range that I target. You can also add an attenuator to (gain knob) to amps to dial down the gain if you have too much in your given gain structure.

Gain is set by the ratio of resistors in the negative feedback loop.

 

[Irvrobinson]

@PENG - I'm not really concerned about the 200W Monolith7 with 28dB gain. I'm using it and it works fine.

But the Purifi 1ET400A based amp I am looking at offers 400W per channel into 4 ohms but only has a 26dB gain. It's a 2 channel amp. The builder says he can increase the gain higher if it would be better for my configuration.

I have two questions:

1. What would be the math to determine what the ext amp gain should be to produce 400W with a 1.4V signal from the Denon 4700?

2. Could increasing the ext amp gain increase distortion on the Purifi 1ET400A based amp?

Thank you!

I'm not PENG, but unless my calculations are incorrect, assuming a 4 ohm load and a maximum 1.4v input signal, the amplifier's gain would have to be approximately 30db. (I can't wait to see if PENG tells me I did this correctly. Crossing my fingers.)

I have no idea how to guess at the answer to your second question. I think it would depend on the amplifier's specific design and its internal gain structure (and I admit I don't understand much about Class D design).

 

[Irvrobinson]

1. All the formula are available in the linked site, but if you have trouble understanding them or not sure how to use them just let me know.

dB calculator for amplification gain and damping (loss) factor of an audio amplifier calculation decibel dB ratio - sengpielaudio Sengpiel Berlin

Calculator damping loss and dB amplification factor gain decibel amplifier audio engineering microphone recordings calculation ratio - sengpielaudio Eberhard Sengpiel

www.sengpielaudio.com

So for the specific example using 1.4 V input and you want to get 400 W output, the math would be as follow:

First, find the required output voltage required for 400 W using the power formula,
P (for a resistor load) = V^2/R, or V = square root of PXR

V=sqrt(400X8) = 56.57 V

Then calculate the Input voltage required for an output voltage of 20 V using the formula:

Vg (voltage gain in ratio, that is multiples) = Vout/Vin

or Vg = 56.57/1.4 =40.4

Now that is a ratio, to express it in dB, the formula is:

Vg (in dB) = 20*log10(Vg in ratio)

Vg(in dB) = 20Xlog10(40.4) = 32.13 dB

2. You have to ask Purifi, as it depends..

Isn't 32.13db an 8 ohm answer?

 

[PENG]

@PENG - I'm not really concerned about the 200W Monolith7 with 28dB gain. I'm using it and it works fine.

But the Purifi 1ET400A based amp I am looking at offers 400W per channel into 4 ohms but only has a 26dB gain. It's a 2 channel amp. The builder says he can increase the gain higher if it would be better for my configuration.

I have two questions:

1. What would be the math to determine what the ext amp gain should be to produce 400W with a 1.4V signal from the Denon 4700?

2. Could increasing the ext amp gain increase distortion on the Purifi 1ET400A based amp?

Thank you!

1. I use my own spread sheet to calculate such things as it is much more flexible, but if you are not familiar with spreadsheet and the related formulae, then you should use online calculator such as the one linked below:

dB calculator for amplification gain and damping (loss) factor of an audio amplifier calculation decibel dB ratio - sengpielaudio Sengpiel Berlin

Calculator damping loss and dB amplification factor gain decibel amplifier audio engineering microphone recordings calculation ratio - sengpielaudio Eberhard Sengpiel

www.sengpielaudio.com

All the formula are available in the linked site, but if you have trouble understanding them or not sure how to use them just let me know.

For the specific example using 1.4 V input and you want to get 400 W output, the math would be as follow:

First, find the required output voltage required for 400 W using the power formula,
P (for a resistor load) = V^2/R, or V = square root of PXR

V=sqrt(400X8) = 56.57 V

Then calculate the voltage gain ratio (in multiples instead of in dB)

Vg (voltage gain in ratio, that is multiples) = Vout/Vin

or Vg = 56.57/1.4 =40.4

As this is a ratio, in you want it in dB, use the formula below:

Vg(in dB) = 20Xlog10(40.4) = 32.13 dB (so this is you answer, get Purifi to do it for 32 dB gain in you want, but make sure you meant 32 dB from the RCA outputs because the AVR-X4700H don't have balanced inputs.

2. You have to ask Purifi, as it depends..

 

[PENG]

Isn't 32.13db an 8 ohm answer?

Yes, for an 8 Ohm resistor load. He mentioned 4 Ohm before, but not in his follow up question, so I have to assume 8 Ohm to be on the safe side.

 

[Irvrobinson]

Yes, for an 8 Ohm resistor load. He mentioned 4 Ohm before, but not in his follow up question, so I have to assume 8 Ohm to be on the safe side.

He did ask about 400 watts into 4 ohms. I calculated 29.13db and rounded up to 30db of gain. (I always round up for requirements. It's a conservative design thing with me.) Since there are several amps out there with a rated gain of 32db, they would probably be the best choices with many AVRs. I'm guessing that's why the amp designers seem to be settling on 32db of gain for single-ended inputs.

I'm smiling... my calculations look correct.

 

[PENG]

He did ask about 400 watts into 4 ohms. I calculated 29.13db and rounded up to 30db of gain. (I always round up for requirements. It's a conservative design thing with me.) Since there are several amps out there with a rated gain of 32db, they would probably be the best choices with many AVRs. I'm guessing that's why the amp designers seem to be settling on 32db of gain for single-ended inputs.

I'm smiling... my calculations look correct.

I was focusing on my calculations and wording in explaining it, and editing... so I did not see your posts until after. If I did, I would have just linked the site/formula as you provided him the number already.